The present invention relates to a laser printer which is capable of printing high grade characters and images by scanning laser beams.
A conventional laser printer whose printing velocity is medium or low usually utilizes a single diode laser beam. On the other hand, a printer in which the printing is effected at an extra-high speed is at present arranged such that the single gas laser beam is intactly employed, or this single gas laser beam is divided into plural gas laser beams by means of an acoustic optical deflector; and both the frequency band region of a modulator and the rate at which a rotating polygonal mirror rotates are reduced by scanning the plural gas laser beams simultaneously.
In either case, however, so far as the gas laser is employed as mentioned above, it is impossible to steer clear of the large consumption of electricity and miniaturize the apparatus. Under such circumstances, there is recently focussed an introduction of a semiconductor laser which is capable of executing direct modulation for itself. However, this kind of semiconductor laser involves defects wherein the wavelength thereof is 1.5.about.2-fold as long as that of the gas laser, which requires a large-sized configuration of the rotating polygonal mirror, and it has been quite difficult to constitute a laser printer by using a single laser beam on account of deteriorated photoconductivity which responds to a long wavelength of the foregoing semiconductor laser.
Such being the case, there is a growing expectation in a method where parallel scanning is effected by making use of a plurality of semiconductor laser beams. Some means for actualizing this end have been disclosed in the specifications of U.S. patent application No. 680497, West German patent application No. P3445751.8, U.S. patent application No. 804940 and West German patent pplication No. P3543472.4 with which some of the inventors of the present invention are associated. However, provided that the printing is performed during the detection of the spacings between plural semiconductor laser beams, it is inconveniently unfeasible to accurately detect it.